The invention relates to open structures and more particularly to the joints of such structures wherein a plurality of intersecting structural members are joined together in a novel way for form a highly stable joint.
When a plurality of structural members intersect at a common point it is usual practice to employ a structural fitting to accommodate the connection of these members one to another. Such a fitting concentrates material and weight at the intersection and alters the structural cross-section of the members at the intersection. For example, in the case of a plurality of intersecting tubular members, the joint fitting may comprise a cast or forged spider of intersecting male plugs adapted for insertion within the inside diameter of each of the tubular members and fastened thereto by means of rivets, bolts, or welding to form a joint wherein all structural member axes converge at one point. In other applications the fitting may comprise a plurality of female bores adapted for receiving the outside diameters of the tubular members and fastened thereto to form a joint. In either case the structural continuity of the members was interrupted by the joint fitting and the cross-section of the member was either increased or decreased. In other instances the tubular members may be squeezed flat at the end and these flat ends joined together by means of bolts, welding or other suitable means.
I-beam and channel section members may be interconnected by means of splice caps which overlay and are attached to the cap portions of the intersecting members, and the web portions connected together by means of clips or brackets. In such joints the cap section has good carry thru, but the webs are totally interrupted and only the clips provide web interconnection.
Thus, it may be seen that even though various shaped cross-section structural members may be used to produce highly efficient structures, maximum structural simplicity and efficiency have not been obtained primarily because of the complexity of joints. Difficulties have continued to exist in developing a highly efficient method of joining intersecting structural members at a common joint. This is particularly true in composite structures wherein the fiber continuity and orientation, upon which performance depends, are seriously compromised in the area of intersections or joints.